1. Description of Prior Art
The present invention relates in general to supplemental restraining systems of motor vehicles, and more particularly, to safety seat belts for restraining passengers upon a vehicle collision or the like. More specifically, the present invention is concerned with woven fabrics for use as a belt proper of the seat belts.
2. Description of the Prior Art
Hitherto, various types of woven fabrics for the safety seat belts have been proposed and put into practical use in the field of motor vehicles and the like. Some of such prior art woven fabrics are of a shock absorbing type which is constructed to absorb shocks applied thereto. That is, as is shown in FIG. 7 of the accompanying drawings, such shock absorbing woven fabric 1 comprises generally warp yarns 2 and weft yarns 3 which are woven in 2/2 or 4/4 twill weaving fashion.
Usually, the warp yarn 2 has a fineness of about 1000 to about 1500 denier, a breaking strength of about 8 to about 10 g/denier and an extensibility of about 10 to 20% in elongation percentage, while, the weft yarn 3 has a fineness of about 500 to 750 denier, a breaking strength of about 5 to about 7 g/denier and an extensibility of about 15 to about 25% in elongation percentage.
Some of such prior art shock absorbing fabrics are disclosed in Japanese Patent Second Provisional Publication 54-20732 and Japanese Patent First Provisional Publication 60-261474. The fabric shown in the 54-20732 publication uses two or more kinds of warp yarns at least one of which is constructed of aromatic polyamide fiber or copolymer fiber of aromatic polyhydrazide-polyamide. The fabric shown in the 60-261474 comprises base yarns and extra yarns which are combined, so that when a shock is applied to the fabric, the base yarns are deformed much greater than the extra yarns.
However, due to the inherent construction, the above-mentioned woven fabrics have failed to exhibit a satisfied initial restraining ability when used as a seat belt. That is, when, due to a vehicle head-on collision of the like, a big force is applied to the seat belt by a belt wearer, the belt is subjected to a considerable elongation causing the belt wearer to largely incline forward. This will be understood from the graph of FIG. 8 in which the relationship between the force applied to the belt 1 and the elongation of the belt 1 is shown. That is, upon application of the force of about 1100 Kg which is common upon a vehicle collision, the belt is subjected to elongation of over 15%.
As is known, the large forward inclination of the belt wearer at such initial stage of the vehicle collision is undesired because of possibility of collision of the belt wearer against a front rigid member. Furthermore, a considerable elongation of the seat belt at such initial stage of the vehicle collision tends to affect the shock absorbing ability possessed by the belt itself.